The present invention relates to a novel positive-working photoresist composition of the chemical sensitization type or, more particularly, to a positive-working photoresist composition of the chemical sensitization type capable of giving a patterned resist layer with high sensitivity and high resolution which is free from the adverse influences of halation and standing waves on the cross sectional profile of the patterned resist layer and has excellent stability of the resist layer before development.
It is a recent trend in the electronic technology to have a requirement for a higher and higher degree of integration of semiconductor devices. This requirement of course cannot be satisfied without improvements in the resolution in the patterning of the resist layer.
In place of the conventional alkali-developable positive-working photoresist compositions comprising, as the basic ingredients, a novolac resin as a film-forming agent and a quinonediazide group-containing compound as a photosensitizing agent, so-called chemical sensitization-type photoresist compositions have been recently developed as a class of promising photoresist materials and are now under way of replacing the conventional photoresist compositions in respect of several advantages. For example, the patternwise exposure of the photoresist composition of this type can be performed by using an ultraviolet light of a shorter wavelength of 200 to 300 nm, such as deep ultraviolet light and excimer laser beams, than for the conventional alkali-developable photoresist compositions while a shorter wavelength of the actinic rays for patternwise exposure is an advantageous condition for the improvement of the resolution in patterning. In addition, the photosensitivity of a chemical sensitization-type photoresist composition can be high by virtue of the nature of the catalytic reaction, which is a kind of a chain reaction, caused by the acid generated by the irradiation of the acid-generating agent with actinic rays for the latent image formation.
While, in the initial stage of development, an alkali-soluble novolac resin, which is the resinous ingredient in the conventional alkali-developable positive-working photoresist compositions, was used also in the chemical sensitization resist compositions as the resinous ingredient, such a novolac resin is not satisfactory therein because the transmissivity of the short-wavelength ultraviolet light through the resist layer containing the novolac resin is so low that the resist layer cannot be exposed patternwise to the ultraviolet light to the bottom of the layer in contact with the substrate surface not to accomplish high-fidelity patterning and not to give an orthogonal cross sectional profile of the patterned resist layer which in this case is rather trapezoidal along with a decrease in the sensitivity and resolution. Accordingly, it is proposed to use, in place of a novolac resin, a poly(hydroxystyrene) resin modified by substituting for at least a part of the hydroxy groups with protective groups having acid-induced dissociability utilizing the higher ultraviolet transmissivity than novolac resins so as to improve the characteristics of the photoresist composition relative to the ultraviolet transmissivity.
As is sometimes the case, positive-working photoresist compositions are used on a substrate having a coating film of a metallic or inorganic substance such as aluminum, aluminum-silicon-copper alloys, titanium nitride, tungsten and the like and the patternwise exposure of the photoresist layer to ultraviolet light may be subject to the troubles of decreased precision and fidelity in fine patterning due to irregular reflection of the light at the surface of the coating layer and occurrence of standing waves so that the reflected light reaches the photosensitive layer behind the pattern on the photomask resulting in localized narrowing of a line pattern or wavy side lines of a pattern.
With an object to solve the above described problems, proposals are made in Japanese Patent Kokai 58-174941, 60-88941, 63-136040, 63-159843 and elsewhere to formulate a positive-working photoresist composition comprising a novolac resin and a quinonediazide group-containing compound with various kinds of halation inhibiting agents when the photoresist composition is to be used on a substrate surface of high reflectivity. Despite the fact that the above mentioned troubles are more serious in the chemical sensitization-type photoresist compositions having higher light transmissivity than the conventional photoresist compositions, no proposals have been made heretofore for a halation inhibiting agent having effectiveness even in a chemical sensitization-type photoresist composition.